Field of the Invention
The present invention relates to an image forming apparatus and a feed control method.
Description of the Related Art
Image forming apparatuses using electrophotographic process technology (such as printers, copiers, and facsimiles) form an electrostatic latent image typically by irradiating (exposing) a charged photoconductor with (to) laser light based on image data. Then, the electrostatic latent image is visualized by supplying toner from a developing device to a photoconductor drum (image carrier) on which the electrostatic latent image has been formed to form a toner image. The toner image is further transferred directly or indirectly to a sheet, and then heated and pressurized by a fuser nip to be fused, and thereby to form a toner image on the sheet.
When a misalignment occurs between a transfer nip and a fuser nip, or when a difference in feed speed arises between the front side and the back side in the fuser nip in the width direction, a difference in feed state arises between both edge portions of a sheet in the width direction. FIG. 1A is a perspective view illustrating a sheet when a difference in feed state arises between its both edge portions in the width direction. FIG. 1B is a perspective view illustrating a sheet when slack occurs in a sheet feed direction. FIG. 2 is a diagram illustrating a state where a sheet having increased slack in a feed direction contacts a peripheral member.
When a difference in feed speed arises between the front side and the back side in a fuser nip in the width direction as illustrated in FIG. 1A, for example, there arises a problem that slack occurs in the feed direction in a sheet that has entered the fuser nip as illustrated in FIG. 1B. In particular, for a sheet such as long paper elongated in the feed direction, difference in speed between the front side and the back side tends to accumulate, increasing slack in the sheet in the feed direction.
When slack in a sheet S in a feed direction is increased, as illustrated in FIG. 2, the sheet S contacts a peripheral member such as an upper guide 60C located at the front of a fuser nip in a fuser 60 that houses a fuser roller 63 and a pressure roller 64. A contacting-side surface of the sheet S is an image forming surface. Thus an unfused image forming surface before entering the fuser nip contacts the peripheral member, causing an image defect. Even when a slack portion in the sheet S does not contact the peripheral member, the rear end of the sheet S may contact the peripheral member, causing an image defect because the rear end of the sheet springs up when released from the transfer nip.
JP 2006-267375 A discloses a configuration in which an entry guide disposed at the front of a fuser nip is moved to press a central portion of a sheet in a width direction. The configuration described in JP 2006-267375 A, however, cannot solve the above problem because when slack occurs in a sheet in a feed direction as illustrated in FIG. 1B, the entry guide does not contact a slack portion.